72 bulletin: museum of comparative zoology. 



But it is impossible at this stage to tell whether the side of the 

 ovum next to the periphery of ovary is covered by but one cell layer, 

 the follicle, or by a limiting epithelium in addition to this. I have 

 never been able to differentiate a limiting epithelium in this position, 

 but the failure could not justify one in denying its existence. When 

 it comes to the formation of the follicular stalk, however, evidence is 

 obtained that is conclusive, for we get the external epithelium of the 

 ovary, which should extend around the ovum independently of the 

 follicle, connecting with it in the clearest possible manner (Plate 3, 

 Figs. 14, 15). Figure 14 shows part of a young ovum that is entirely 

 outside of the ovarian wall, but which is not yet attached to it by a 

 stalk. On the left the ovum is attached to the germinative epithelium, 

 as the tangential section of a much younger egg (ov'go.) shows. On 

 the right it joins stalk tissue which has not yet assumed its typical 

 appearance. Between the two are cells which make up both the fol- 

 licle and the wall of the ovary, and will probably differentiate into 

 follicle and stalk tissue. Figure 15 represents the same region in an 

 older ovum, where the stalk tissue presents its characteristic structure 

 and is seen to be directly continuous with the follicular epithelium. 

 From these facts the conclusion seems justified that in the adult 

 Distaplia ovary, just as in the developing one, we have no peripheral 

 limiting epithelium. 



One feature that is not usually encountered in other species, but is 

 quite conspicuous in the ovary of this one, is the corpus luteum (Fig. 

 5, cp. hit.). This structure is merely the part of the follicular cover- 

 ing of the egg which remains behind when the latter is extruded from 

 the ovary. It will be described in detail after the origin of its con- 

 stituent elements has been considered. 



The oviduct (Plate 2, Fig. 9, ov'dt.) is a narrow, thin-walled tube 

 extending up the right side of the abdomen and in immediate contact 

 with the ectoderm. Throughout its extent the vas deferens (va. df.) 

 is closely appressed to its deep wall. The most striking peculiarity 

 of the oviduct is that its diameter, even when distended by the passage 

 of an ovum, is very much less than the normal diameter of the ripe 

 egg. Accordingly, when the egg is passing through the duct, it is 

 greatly distorted, assuming the shape of a sausage (Plate 3, Fig. 17). 

 In this figure the ovum occupies a part of the oviduct, all of the 

 cavity proper of the ovary, and also the entire cavity enclosed by the 

 stalk tissue and its own follicle. The point where the stalk tissue 

 joins the germinative epithelium lining the deep wall of the ovary 



